These automatic whatevers that y'all come up with are never helpful. People who read long documents already know how to mark their place, using a method they choose. If you invent an obnoxious little flag thing that pops a comment box up in my face when
I start my working day, you need to make sure it's easy to turn off!
Note that no one here has invented "pick up where you left off." The vast majority of posters are volunteers and we do not represent Microsoft. If you want to make a suggestion for Microsoft, go to the forum at
http://word.uservoice.com.
A workaround involving a registry hack has been suggested in this thread (and it is also marked as Answer). Try it if you wish.